1. Field of the Invention
The present invention relates to a cooling structure, an image projection apparatus, an electronic device, and a cooling device.
2. Description of the Related Art
As a technique of cooling a heat source, a method of putting a heat sink to the heat source to expand a heat releasing area, and of blowing cooling air onto a heat releasing unit has been known. As a technique of further improving the cooling efficiency, for example, fabricating the heat sink with a highly thermal conductive material has been practiced. By fabricating the heat sink with highly thermal conductive material, it becomes possible to spread the heat transmitted from a contact unit in contact with the heat source uniformly to the entire heat sink. As a result, the heat releasing area can be enlarged, and therefore, the heat source can be cooled efficiently.
Moreover, enlarging the contact area of cooling air and the heat sink is also effective. The heat sink heated by receiving heat from the heat source is cooled at a portion that contacts with cooling air. Therefore, it becomes possible to improve the cooling efficiency by expanding an area that contacts with cooling air. Moreover, a method of arranging fins on a heat sink has been known as a method of expanding the contact area. By arranging fins in a small pitch and blowing cooling air between respective pitches, a contact area that contacts with the cooling air is expanded, and thus the cooling efficiency is improved.
Furthermore, a forcible cooling method of cooling the heat sink using a fan has also been adopted. Cooling performance is dependent on a wind velocity of air that passes through between the pitches of the fins. Therefore, to improve the cooling performance, it is necessary to increase the speed of the air that passes through between pitches, and a higher cooling effect can be acquired with the forcible air cooling rather than air cooling without blower. As a forcible air cooling, a method of using a fan is common, and especially a cooling structure in which a sirocco fan having high static pressure is arranged so as to oppose to the fins, and air blown out from the sirocco fan blows the fins of the heat sink directly is considered common (Japanese Laid-open Patent Publication No. 2008-134432, Japanese Patent No. 4901595, Japanese Patent 4927923).
However, in the above conventional cooling method, when the cooling efficiency is to be improved structurally, it is required to enlarge a surface area of the heat sink, or to prepare a more powerful large fan to improve the cooling efficiency, and there has been a problem that the structure increases in size. Therefore, in any case, the structure increases in size and weight, and there has been a problem that it is difficult to be equipped inside compact and lightweight electric devices.
Moreover, in the method of arranging the fins in a small pitch, because the cooling air passes through between the pitches of the fins, air resistance increases if the fins are arranged in a small pitch. Because the cooling performance is dependent on an amount of air, if the air resistance increases, the amount of the air that passes through the fins decreases. Therefore, there has been a problem that it is difficult to use the air that has passed through the fins, for cooling other components. That is, when forming a structure in which a fan, a heat releasing unit, and other cooling targets are aligned in series in the above order to cool not only the heat releasing unit but also the other cooling targets at the same time using cooling air blown out from the fan, if the fins are arranged in a small pitch, the cooling performance for the heat releasing unit is enhanced but it is difficult to cool the cooling targets positioned downstream relative to the heat releasing unit.
Therefore, in the conventional method of improving the cooling performance by arranging fins in a small pitch, a structure in which the target to be cooled by a fan is only a heat releasing unit is common, and even if it is structured such that the other components are cooled using air that has been used to cool the heat releasing unit, the cooling performance therefor cannot be expected. Moreover, when fins are designed to have a complicated shape, there has been a problem that cost of the fins increases. Therefore, ideally, such a method of expanding the surface area of the heat releasing unit with a simple shape is demanded.
Therefore, there is a need to offer a cooling structure that enables to enhance the cooling performance of a heat releasing unit, and to cool, at the same time, a cooling target positioned downstream relative to the heat releasing unit using air that has been used to cool the heat releasing unit.